Ethernet is a family of computer networking technologies for local area networks (LANs). Ethernet was commercially introduced in 1980 and standardized in 1985 as IEEE 802.3 by the Institute of Electrical and Electronics Engineers (IEEE). Ethernet has largely replaced competing wired LAN technologies.
The Ethernet standards comprise several wiring and signaling variants of the Open Systems Interconnection (OSI) physical layer in use with Ethernet. The original 10BASE5 Ethernet used coaxial cable as a shared medium. Later the coaxial cables were replaced by twisted pair and fiber optic links in conjunction with hubs or switches.
A switch is a telecommunication device which receives a message from any device connected to it and then transmits the message only to that device for which the message was meant. This makes the switch a more intelligent device than a hub (which receives a message and then transmits it to all the other devices on its network). The network switch plays an integral part in most modern LANs.
An Ethernet device that is connected to a switch has to keep the link activated, since when the link is lost on a certain port, the switch will no longer send data to that port. The device needs to send a single pulse or a series of pulses which are called Link Integrity Test (LIT) pulses in the 10BASE-T terminology. 10BASE-T was designed for point-to-point links only, and all termination was built into the Ethernet device. Higher speed connections use initial auto-negotiation to negotiate about speed, half duplex and full duplex and master/slave. This auto-negotiation is based on pulses similar to those used by 10BASE-T devices to detect the presence of a connection to another device. When the auto-negotiation has finished, the devices only send an idle byte when there is no data send, to keep the link up.
Power-over-Ethernet (PoE) is an active standard (IEEE 802.3.af and IEEE 802.3.at) which allows a PoE supply to provide electrical energy to detached networked electrical consumers like routers, switches, printer spoolers, et cetera over their standard Ethernet cable connection. Here actual standardization is going to support power levels even above 50 W per Cat5 connection. Currently, discussions are coming up to use the same standard for all kinds of low power consumers like lighting equipment (sensors, switches, light sources) or entertainment appliances like active speakers, internet radios, Digital Versatile Disk (DVD) players, set-top boxes and even television (TV) sets. PoE phones and PoE powered control devices are becoming already common practice in offices.
As the industry is more and more discussing direct current (DC) distribution as an efficient future alternative for the well known alternating current (AC) mains, also supplying power to lighting devices via PoE may get used widely.
However, if the detached networked electrical consumers are in their standby state they still take some power from the PoE power supply to keep internal processing alert to be able to react on any Ethernet activity. Thus, even in the standby state of the detached networked electrical consumers the power consumption is quite high. In current systems the link is kept fully active, which consumes a lot of energy. In a lighting system using PoE for powering the luminairs this can add up to several hundreds of mW standby power even when the luminairs are switched off.